Photoengraving equipment



June 10, 1952 T. HOMMEL PHOTOENGRAVING' EQUIPMENT 1O Sheets-Sheet 2 Filed Dec. 4, 1948 INVENTOR (L E M M 0 H E R O D O E H ATTORNEY June 10, 1952 'r. HQMMEL PHOTOENGRAVING EQUIPMENT 10 Sheets-Sheet 3 Filed Dec. 4, 1948 I r t'lllnlllE I Iii ii ILII I INVENTOR THEODORE HOMMEL ATTORNEY June 10, 1952 T. NON PHo'rmNGRAv-Im EQUIPMENT I 10 Sheets-Sheet 4 Filed Dec 4, 1948 FIG. 7

FIG.

FIG.

INVENTOR THEODORE HOMMEL ATTORNEY 10 Sheets-Sheet 5 INVENTOR HOMMEL as Q. q l

ATTORNEY THEODORE T. HOMMEL pao'rdsucmvmc EQUIPMENT June 10, 1952 v Filed Dec. 4, 1948 June 10, 1952 'r. HOMMEL 2,600,295

aowosucmvmc EQUIPMENT Filed Dec. 4, 1948 1O Sheets-Sheet 6 W a e W/ THEODORE HOMMEL.

June 10, 1952 1 HOMME L PHOTOENGRAVING EQUIPMENT 1O Sheets-Sheet 9 Filed Dec. 4, 1948 TH EOOORE INVENTOF? HOMMEL June 10, 1952 T. HOMMEL.

PHOTOENGRAVING EQUIPMENT 10 Sheets-Sheet 10 Filed Dec. 4, 1948 FIG.27

FIG. 24

v: mm m mm R o w w m A E R I O D 0 m 6 T a m G F w r '1 H 3 7 2 I W V Z 0 2 m 7 m Patented June 10, 1952 UNITED STATES PATENT V'OFFICE Pnoro NG vING EQUIPMENT Theodore HommeL'Webster Groves, Mo., assignor to Uni-versa'lMatch Corporation, St. Louis, Mo..

a corporation of Delaware Application December 4, 19.48, Serial No. 63,514

1 .16 Claims.

'This invention relates in general to certain new and useful improvements in photoengraving equipment and, more particularly, to a type of photo-composing machine which may be referred to as a cylinder step-up machine.

In making photoengraved printing rolls and arcuate plates for use in conjunction with intaglio 'ofiset, or letter-press printing presses, it is common practice to sensitize a carefully machined and polished flat or cylindrical surface by applying thereto a suitable light sensitive emulsion or chemical and thereupon exposing the sensitized surface through a suitable negative by conventional photographic technique, so that the design on the negative will b photographically imprinted upon the sensitized surface. 'Thereafter, the sensitized surface is subjected to a conventianal series of chemical processes or developed, as it is commonly called, and, as a result, the design is etched upon'the surface of the roller orpl i In this process, the sensitized roller must be mountedin some suitable form of holding means and'the negative secured andsnugly placed thereover under dark room conditions, the negativ being held in place by some appropriate chemical means. With the ne ative and holder thus securely held, the exposure is madeby turning on a suitablelighit source for a predetermined period of time. A proper exposure technique requires very precise control of the length of .exposure time and the intensity of light brought to bear upon the negative and it is essential that the .operator be able to vary or adjust these conditions to meet variations in the density of the negative and other specific requirements of a particular piece of Work. Although efforts have been made in the past to control light intensity by various expedients, such as filters, screens,

and the employment of groups of light sources which'may be used in vary numbers and combinations, these expedients have all proved highly unsatisfactory and it has become common .practice'to employ a light which. is as constant in intensity as may be possible to obtain, relying for variations and control upon exposure time. It is, therefore, essential in any'photoengraving apparatus of the type here under discussion to provide means for varying'the exposure time over fairly wide limits and yet make provision .for accurate control, so that any interval selected will be precisely timed.

In cylinder step-up machines, the sensitized emulsion'lies upon the surface of a cylinder and the cylinder and its uperposed negative must be held stationary in order to prevent thedanger of improper registration between the negative and the sensitized surface during exposure. It is obvious, therefore, that certain portions of the sensitized surface and negative will be relatively close to the light source, wherea other portions will be comparatively remote. Even where an elongated mercury arc tube is used as a light source and is placed in radially spaced parallel relation to the cylindrical surface, that longitudinally extending band of the exposure "area which lies directly in radial alignment with the light will receive greatest exposure while the lateral portions of the exposure area will receive appreciably reduced exposure. Some efforts have been made to solve this problem by placing a multiplicity of spaced parallel tube in an arcuate pattern around the entire exposure area, but

such apparatus has been found to be expensive, difiicult to use, and, what is most important, un-

reliable, because it is virtually impossible to match a plurality of light sources, so that each tube or bulb has the same light intensity within close enough limits for accurate photoengraving results.

It is hence the primary object of the present invention to provide a photo-composing machine of the cylinder step-up type which is simple, compact, and economical and is capable of extremely precise construction and operation.

'It is a further object of the present invention to provide a machine of the type stated-in which all portions of the negative will be subjected to precisely the same degree of light intensityduring exposure.

It is an additional object of the present invention to provide a machine of the type stated in which the exposure interval can be varied over a relatively wide range of adjustment and any selected exposure interval Will'be precisely controlled within extremely close limits.

It is also an object of the present invention to provide a machine of the type stated which is fully automatic and is so constructed that faulty exposures due to mistakes of the operator, malfunctioning of the machine, or other accidental causes are substantially eliminated or prevented.

exactly the same length of time, producing absolutely uniform exposure throughout the exposed area.

With the above and other objects in view, my invention resides in the novel features of form' construction, arrangement, and combination of parts presently described and pointed out in the claims.

In the accompanying drawings:

Figure 1 is a front view of a cylinder step-up machine constructed in accordance with and embodying the present invention;

Figure 2 is a side elevational view of the ma chine taken from the left in Figure 1;

Figure 3 is a fragmentary side elevational view taken from the right in Figure 1;

Figure 4 is a transverse sectional view taken along line 4-4 of Figure 2;

Figures 5, 6, 7, 8, and 9 are transverse sectional views taken along lines 5-5, 66, l-l, 88, and 9-9, respectively, of Figure 4;

Figure 10 is a transverse sectional view taken along line IO| 0 of Figure 6;

Figure 11 is a transverse sectional view taken along line ll|l of Figure 9;

Figure 12 is a transverse sectional view taken along line |2l2 of Figure 3;

Figure 13 is a fragmentary sectional view taken along line l3-l 3 of Figure 9;

Figure 14 is a front View of the control panel;

Figure 15 is a fragmentary sectional view taken along line l5i5 of Figure 2 and showing a detail top plan view of the sweep counter mechanism forming a part of the present invention;

Figure 16 is a fragmentary sectional view taken along line Iii-l6 of Figure 2 and showing a detail elevational view of the sweep counter mechanism forming a part of the present invention;

Figures 17, 18, and 19 are sectional views taken, respectively, along lines I1-l'i, l8|8, and 19-19 of Figure 16;

Figure 20 is an enlarged detail view illustrating the operation of the ratchet of the sweep counter mechanism;

Figure 21 is a fragmentary sectional view taken along line 2|2I of Figure 14, showing in sectional detail the cycle selector switch forming a part of the present invention;

Figure 22 is a sectional view taken along line 22-22 of Figure 21;

Figure 23 is a wiring diagram, showing the electrical connections between the various electrical components of the machine;

Figure 24 is an end elevational view of a modified form of positioning mechanism for the sweep control switches;

Figures 25 and 26 are front elevational and top plan views, respectively, of the modified form of positioning mechanism shown in Figure 24; and

Figure 27 is a fragmentary sectional view taken along line 21-21 of Figure 24.

Referring now in more detail and by reference characters to the drawings, which illustrate practical embodiments of the present invention, A designates a cylinder step-up machine comprising a support stand I having a rectangular horizontal top frame 2 constructed preferably of welded angle iron and provided at its four corners with vertical depending legs 3. Attached to, and extending horizontally between, said legs 3 a short distance upwardly from their lower ends is a rectangular sub-frame 4 also formed of angle iron and supporting a heavy gauge sheet iron shelf 5. For greater rigidity, the sub-frame 4 is 4 tied into the top frame 2 by vertical support rods 6 extending therebetween approximately midway of the ends. Bolted or otherwise rigidly secured upon and extending across the top frame 2 is a bed-plate I provided in its upper horizontal face with transversely extending slide grooves 8 for engaging conventional ball-bearing rollers 9 operatively mounted upon the lateral faces of slide blocks 9 supportingly mounted on the under side of a cylinder holding apparatus B preferably of a type more fully disclosed and described in co-pending application for United States Letters Patent, Serial No. 668,178, filed May 8, 1946, now Patent No. 2,547,527, issued April 3, 1951.

For present purposes, it is sufficient to point out that the cylinder holding apparatus B comprises an elongated machine base In having longitudinally extending ways ll. Slidably mounted for movement into various relative positions along the base 10 is a pair of mandrel supporting slides l2, 12, provided at their lower extremities with shoe portions 13, 13, having locking means [4, 14, whereby the slides l2, 12, may be locked rigidly in any suitable position along the ways H.

Precisely journaled in, and extending horizontally through, the upper ends of the slides l2, I2, is a mandrel 15 adapted to support a sensitized cylinder C which is to be photoengraved. Mounted in, and projecting vertically from the upper ends of, the slides l2, l2, are posts [6. [6, for suitably receiving and supporting accurately aligned clamps ll, l1, respectively, designed to hold the negative n. The clamps ll, ll, are so arranged that the negative n can be mounted accurately therein for proper alignment with the cylinder. Swingably mounted upon the base if] respectively in forwardly and rearwardly spaced parallel relationship to the mandrel I5 are negative holding bars [8 provided upon their exposed faces with cementitiously secured soft rubber contact shoes 19 having an externally presented continuous peripheral lip 20 and an elongated oval or channel-shaped groove 21 communicating through a flexible vacuum line 22 to a vacuum pump 23 mounted upon the subframe shelf 5 and drivingly connected by means of a suitable belt 24 to an electric motor 25, all as best seen in Figures 1 and 4.

The mandrel [5 projects outwardly from the slides l2 and extends through a roller bearin 26 mounted upon the upper end of a supporting post 27, which is, in turn, rigidly bolted upon the base IE Beyond the roller bearing 26, the mandrel I5 is mounted in a second roller bearing 28, which is likewise supported above the base ID by a head stock 29. Keyed or otherwise rigidly fixed to the portion of the mandrel l5 which extends between the bearings 26, 28, is a disk-like positioning collar 30 having a plurality of equally spaced annularly arranged tapered apertures 3| each adapted to receive the tapered locking tongue 32 formed upon one end of a horizontally shiftable locking rod 33 suitably mounted in, and extending through, a cylindrical enlargement 34 integrally formed in the base of the head stock 29. Swingably mounted upon the lateral end face of the base [0 adjacent the head stock 29 is an operating lever or handle 35 integrally provided on its inner end with an upwardly projecting leg 36 which rockably engages the rod 33, so that, when the handle 35 is swung upwardly toward vertical position, the leg 36 will rock outwardly, withdrawing the rod 33 and the tapered locking tongue .5 32 from engagement with one of the apertures 3| of the disk 30.

Rigidly mounted upon the rear face of the top frame 13 is a blower 37 conventionally driven by an electric motor 38 and connected at its discharge end by means of a vertical duct 30 to a horizontal air outlet 40 located just above the bearing '26 and in approximate parallelism with the mandrel l so as to direct a cooling blast of air horizontally across the upwardly presented face of the negative to prevent overheating thereof during exposure. Rigidly mounted to the opposite transverse end margins of, and extending vertically above and below, the bedplate I are trunnion plates 4| provided adjacent their upper ends, and upon their inwardly presented faces, with horizontal trunnions 42, which are precisely aligned axially with each other and the horizontal axis of the mandrel l5 and are adapted for rota-tably supporting relatively large sprocket wheels 43, 43, drivingly connected, respectively, by sprocket chains 44, 44, to driving sprockets 45, 45, which are, in turn, pinned upon a horizontal drive shaft 46 journaled at its ends in, and extending horizontally between, the lower portions of the trunnion plates 4| in upwardly spaced parallel relation to the sub-frame shelf 5. Bolted rigidly upon and offset from the inner face of the sprocket wheel 43 is a radially projecting arm 41, and similarly bolted to the inner face of the sprocket wheel 43' is a bracket plate 48 integrally provided with a horizontally inwardly extending bracket arm 49 terminating at its inner end in an integral vertically extending end plate 50, to which is bolted a radially extending arm 5| of substantially the same size and shape as the arm 41 and disposed parallel thereto and in marginal registration therewith.

Securely bolted at their opposite ends to, and extending horizontally between the upper ends of, the arms 41, 5|, are relatively heavy angle sections 52, 53, transversely connected at uniformly spaced intervals along their length by relatively thick vertical truss plates 54 which project at their lower margins substantially below the lower margins of the angle sections 52, 53, and have an upwardly curved bottom margin 55 of substantially parabolic contour for supporting an inverted light trough 56 extending longitudinally between, and abutting at its ends against, the inner faces of the arms 41, 5|. Along its longitudinal margins, the light'trough 56 is provided with outwardly projecting flat flanges 51 for securement to the outer portions of the under faces of the truss plates 54 and are held down by relatively heavy flat runner bars 58 which are transversely connected at their outer ends by shield plates 59 which extend inwardly over the downwardly opening face of the light trough 56 for a substantial distance inwardly from the arms 41, 5|, leaving a centrally located rectangular light opening or aperature 60. Operatively mounted, so as to lie symmetrically within the light trough 56, are electrical socket elements 6| for receiving the ends of a tubular light source 62, such as a mercury vapor discharge lamp or high wattage fluorescent tube, for example. The arms 41, 5|, are also provided with apertures J, f, located in alignment with the axis of the tubular light source 62, as best seen in Figure and for purposes presently more fully appearing.

When the light source 62 is energized or lit, it will generate a very intense amount of light and at the same time will reach a very high temperature. For this reason, the downwardly presented face of the light trough 56, which is parabolic in cross sectional shape, is preferably polished or otherwise treated to become light reflective; whereas, the opposite surface is left dull in order to radiate and thus dissipate as much heat as posible. It will also be noted in this connection that the supporting structure for the light trough is relatively open so as to provide for maximum ventilation. Finally, a conventional blower 63 is bolted or otherwise suitably mounted upon the bracket arm 49 and is conventionally driven by an electric motor 64. The blower 63 is connected at its discharge end to an outlet duct 65 which extends through the aperture 1 in the arm 5| and discharges a strong high velocity draft of air from the blower 63 along the light source 62 and out through the aperture ,1" in the arm 41.

The runner bars 58' project marginally outwardly beyond the longitudinal edges of the light trough 56 to provide track-Ways for ball bearing rollers r operatively mounted at spaced intervals in shutter slides 66 which are integrally provided on their upper faces with racks 6"! and upon their lower faces with downwardly projecting ribs 68. Marginally bolted to the ribs 68 and extending transversely across the light trough 56 is a shutter plate 69 disposed for snugfitting sliding abutment against the under face of the runner bars 58. It should be noted in this connection that this abutment must be sufficiently tight to prevent light leaks, but, at the same time, should permit relatively free sliding movement of the shutter plate to and fro over the left hand half of the aperture 66.

Similarly mounted along the right hand end of the runner bars 58 are shutter slides 66 substantially identical with the previously described shutter slides 66 and likewise being integrally provided upon their upper faces with racks 6i and upon their upper faces with racks 61 and upon their under faces with depending ribs 68 for receiving a shutter plate 69 which extends transversely across the light trough 5.6 and is adapted for slidable movement to and fro across the right hand half of the aperture 66. Rigidly mounted upon and extending transversely between the angle sections 52, a short distance inwardly from the arm 5|, is an inverted U- shaped journal bracket Ill for rotatably supporting a shaft H which projects transversely therethrough and is provided at its outwardly proecting ends with pinions 12, 12, for meshing engagement, respectively, with the front and rear racks 61, so that when the shaft H is rotated in a counter-clockwise direction (reference being made to Figure 4) the shutter slides 66 and the shutter plates 69 carried therebywill be shifted longitudinally to the right to cover the left hand side of the aperture 66 and, contrariwise, when the shaft TI is rotated in the opposite or clockwise direction the shutter plates 69 will be shifted to the left uncovering the left hand side of the aperture 60.

The rearward pinion 12 is also in meshing engagement on its upper side with a downwardly presented rack bar 13 which is securely bolted to a long slide bar 14 which, at its left hand end, extends through and is shiftably mounted in a slide block 15 which is, in turn, rigidly bolted to the rear angle section 52. At its right hand end the slide bar 14 extends through, and is slidably mounted in, a second slide block 16 and is similarly provided upon its under face with 9. depending rack bar 11 which meshes with a pinion I8 pinned upon one extending end of a shaft I9 journaled in and projecting transversely through a second inverted U-shaped journal bracket 89 and is rigidly provided at its forwardly projecting end with a companion pinion I8. On their under sides, the pinions I8, 18, mesh with operatively mounted idler gears 8I, 8|, which in turn are in meshing engagement upon their under sides with the racks 61 of the right hand shutter slides 68'. When shaft 79 and the pinions I8, 18', are rotated in a counter-clockwise direction (reference being again had to Figure 4), the idler gears 8|, 8|, will rotate in a clockwise direction causing the racks 6i and the shutter slides 66, together with the shutter plates 69 carried thereby, to shift to the left, covering the right-hand half of the aperture 60, and, contrariwise, when the shaft I9 is rotated in a clockwise direction, the shutter plates 69 will be correspondingly shifted to the right to uncover the right-hand half of the aperture 59. It should be noted in this connection that, as the pinion 18 rotates in a counter-clockwise direction, the slide bar 74 and its associated rack members I3, I1, will be shifted to the left, transmitting counter-clockwise movement to the pinion I2 and its associated shaft II. Thus, it is to be seen that the shutter plates 69' will move toward and away from each other simultaneously to open and close the light aperture 60. It should furthermore be noted in this connection that the various tooth-ratios of the racks 61, 91, 13, I1, and the pinions I2, 12, '19, I8, and the idler gears 8I, BI are such that the shutter plates 69, 69, will be brought into light-proof endwise abutment approximately at the center line of the light aperture E when they are shifted into closed position, and the shutter plate 69 is finally provided around its abutting margins with a laterally projecting lip which overlaps the abutting margin of the shutter plates 59 when the shutter plates 69, B9, are in closed position so as to insure against light leakage. Mounted upon and extending between the angle sections 52 to the right of the shaft 19 is a shutter operating solenoid 92 having a plunger rod 83 connected at one end to the slide bar 74 and biased to the left by a strong compression spring 84 which abuts against a bracket arm 85 forming part of the solenoid frame, all as best seen in Figure 4. The arms 47, El, and associated structure, including the lamp 62 and shutter plates 69, 69, may, for convenience, be referred to as the lamp assembly L.

Bolted or otherwise securely mounted upon the sub-fram shelf 5, adjacent the forward edge thereof, is a main-drive electric motor 85 having a rearwardly extending drive shaft 81 provided with a drive pulley 88, which is, in turn, connected by a flexible belt 89 to a driven pulley 90 keyed upon the forward end of a shaft 9I forming part of a conventional gear reduction transmission or drive assembly 92 having a rearwardly projecting transmission shaft 93, which is, in turn, provided with a bevel gear 94 for meshing engagement with a companion bevel gear 95 pinned to the shaft 46.

Pinned to the shaft 9| inwardly of the driven pulley 90 is a spur gear 96 in meshing engagement with a second spur gear 91, which is, in turn, pinned upon a horizontal jack shaft 98 journaled in a bearing post 99 and provided on its rearwardly projecting end with a bevel gear I 00 for meshing engagement with a companion bevel gear IOI pinned upon the projecting end of a control shaft I02 journaled in and extending between bearings I03, I04. For a relatively extensive portion of its length intermediate the bearings I03, I04, the control shaft I02 is provided with a diametrally enlarged externally threaded portion forming a lead screw I05. Welded upon the upper face of the sub-frame shelf 5 is an L- shaped member I06 having a vertically upwardly projecting rail I01 disposed in downwardly spaced parallel alignment with the axis of the control shaft I02. Slidably mounted upon the rail I0'I for to-and-fro movement lengthwise therealong in a slid block I08 which is bolted along its upper face to a nut member I09 threadedly mounted on the lead screw I05. Also bolted upon the lateral faces of the guide block I08 are two upwardly extending L-shaped brackets H0, H0, respectively having forwardly and rearwardly extending horizontal arms III, III, for carrying vertically adjustable threaded posts H2, H2, held in place by conventional lock nuts H3, H3, and being provided on their lower ends with contact shoes I I4, I I4, all as best seen in Figure 11 and for purposes presently more fully appearing.

Securely mounted upon the upper face of the sub-frame shelf 5 in uniformly spaced longitudinal alignment along the path of movement of th contact shoe II4 are seven identical microswitches H5, H6, H1, H8, H9, I20, and I2I, and similarly mounted in forward alignment with the middle micro-switch H8 is a micro-switch I22 disposed in the path of movement of the contact shoe II4.

When the main drive motor 86 is energized, the shafts 9|, 93, will be turned and the shafts 46 and I02 will be correspondingly rotated. The rotation of the shaft 46 will, in turn, be transmitted through the sprocket chains 44 to the sprockets 43 and the arms 41, 5I, will accordingly be rocked forwardly or rearwardly as the case may be. At the same time, the nut I09 and the slide block I08 carried thereby will traverse along the lead screw I05 and the contact shoes H4, H4, will ride over the rollers H5, H0, H1, H8, H9, I20, I2I, and I22. The micro-switches H5, H6, H1, H8, H9, I20, I2I, and I22 are normally in the position shown in the wiring diagram, Figures 23, which, for convenience, may be referred to as the closed position. Actually, the machine A is so set up that when the lamp assembly L is in vertical position, as shown in full lines in Figure 4, the contact shoes H4, H4, will lie astride the middle micro-switches H8 and I22. For convenience, this position may be referred to as the zero position and one complete cycle of movement of the lamp assembly L forwardly to the limit of forward travel, backwardly through zero position to the limit of backward travel, and thence forwardly again to zero position may be referred to as one sweep. Furthermore, the gear reduction drive assembly 92 is preferably so constructed that when the main drive motor 86 rotates the pulley in a counterclockwise direction (reference being made to Figur 4), the shaft 46 will be rotated in such direction that the lamp assembly L will swing arcuately forwardly. Simultaneously, the nut I09 and the slide block I08, together with associated structure, will shift to the right, and, contrariwise, as the motor 86 reverses its direction, the lamp assembly L will swing rearwardly and the slide block I08 will correspondingly move to the left.

Inasmuch as the lamp assembly L always swings at a uniform speed along the periphery of its arc of travel, the area of exposure can be controlled by the length of arc selected for the sweep and the length of exposure can be controlled by the number of sweeps made during a single exposure. Hence, the machin A is provided with controls, presently to be more fully described, whereby any selected number of sweeps can be automatically made and the arc of movement during each sweep can be limited to either 60, 120, or 180, that is to say, the total are traversed by the arms 41, I, between the forward and rearward limits of travel will be either 60, 120, or 180, as th case may be. The limitcontrol of this are of movement is a function of the micro-switches H5 to I2l, inclusive. If the 60 sweep is selected, by means and in a manner presently to be more fully described, the shoe II 4' will contact the roller II9 of the microswitch H9, which will, in turn, initiate a series of circuit rearrangements, also more fully discussed hereinafter, to the end that the direction of rotation of the motor 86 will be reversed and the slide block I08 will be traversed to the left past the zero position until the shoe II4 contacts the roller 1' of the micro-switch III, which will, in turn, initiate a series of circuit rearrangements, again reversing the motor 86. Thus, the slide block I08 and the shoes H4, H4, carried thereby will shuttle back and forth between the switches II'I, H9, and gearing and various tooth-ratios in the machine A are such that the lamp assembly L will, under such circumstances, travel through an arc of 60, i. e.,

on each side of zero position. If either a 120 and. 180 sweep is desired, manually operable control switches, presently to be described, may be optionally actuated to render the switches H1, H9, inoperative as limit switches and cause the switches H6, I20, or H5, I2l, as the case may be, to assume the sweep limit-control function.

The motor shaft 6'! also projects forwardly from the main drive motor 65 and is provided with a brake drum 123 which runs between two diametrally opposed arcuate brake shoes I24, I24, respectively carried by brake arms I25, I25, rockably mounted, as at I26, I26, upon and extending vertically upwardly from a pivot block I21, which is, in turn, mounted on a base plate I28 which projects laterally therefrom and on its projecting end is provided with a solenoid I25 having an upwardly extending plunger rod I30. Rockably pinned to the upper end of the brake arm I25 is a link rod Isl extending over the brake drum I23 and projecting loosely through the upper end of the other brake arm I25. On such projecting end, the link rod I3I is threaded to receive a nut I62 and washer I33 which abuts endwise against a relatively strong compression spring I34, which, in turn, abuts at its other end against the brake arm I25, so that the brake arms I25, I25, are normally biased toward each other and the brake shoes I24, I 24, tightly grip the brake drum I23. Welded or otherwise rigidly mounted on the brake arm I25 below the link rod I31 is an inwardly extending block I35 provided with a short pivot stud I35 for pivotally supporting a rocker arm I31, which is also rockably connected to the link rod It! by a I38, which is spaced upwardly a substantial distance from the pivot stud I56. At its free end, the rocker arm I 31 is rookably connected by means of a pin I39 to the upper end of the solenoid plunger rod I36, all as best seen in Figure 13.

The solenoid I29 is connected in parallel with the electrical leads to the main drive motor 86, so that, as the motor 86 is energized, the solenoid I29 will likewise be energized, drawing the plunger rod I39 downwardly. The rocker arm I61 will also be swung downwardly by the pivot stud I36. This rocking movement of the rocker arm I31 will cause the pivot stud I36 and the pin I38 to move in opposite directions relative to each other and, in effect, shift the link rod I3] to the left against the bias of the compression spring I 34. This action will swing the upper ends of the brake arms I 25, I25, away from each other and accordingly shift the brake shoes I24, I24, out of gripping engagement with the brake drum I23, thereby releasing the motor shaft 81 and permitting it to commence rotation. As soon as the circuit to the motor 86 is broken and the motor is de-energized, the solenoid will instantaneously release the plunger rod I30, so that the compression spring I34 will instantly shift the brake arms I25, I25, toward each other again and the brake shoes I 24, I24, will again grip the brake drum I 23, bringing the motor shaft 37 to an instantaneous stop without permitting any over travel. It should be noted in this connection that the compression spring I34, the brake shoes I24, I24, and intermediate associated parts must be very sturdi-ly constructed because the motor shaft 81 and all of the components driven thereby, including the lamp assembly L, will possess a substantial amount of inertia, requiring a fairly heavy and positive braking action in order to bring the mechanism to an instantaneous stop when the motor is. deenergized.

Inasmuch as it is desirable to bring the entire mechanism to a precise and immediate stop whenever the motor 86 is ole-energized, it is essential to prevent backlash in the sprocket chains 44. Therefore, the sprocket chains are trained over small idler sprockets I 40 which are-rotatably carried by small brackets I4I, which are, in turn, mounted for shifting adjustment upon the bed plate I and project rearwardly beyond the rear edge thereof. By a slight amount of forward or rearward adjustment of the brackets I 4| from time to time, any backlash or looseness in the sprocket chains 44 may be eliminated.

Suitably mounted upon the bed plate 1, at the forward left-hand corner thereof, is a control box I42 having a forwardly presented vertical panel 543 and a rearwardly inclined main panel I44. Set into the panel I44 is a vacuum gauge I45 operatively connected to. the vacuum pump and having a visible dial I45 and an indicating needle 54?, so that the operator may at all times control and adjust the amount of. vacuum in the vacuum lines 22. Also mounted in the panel I44 are four two-point single-blade toggle switches !5I, I52, I53, I54, which are respectively labeled sweep reset, sweep set, sweep stop, sweepv start. Operably mounted within this control box I42 is a so-called sweep counter mechanism I 55 and mounted upon the panel I 44 is a cycle selector switch I56, both presently to be more fully described. Also set into the panel I44 are three single-pole double-throw toggle switches I57, I58, I56, respectively labeled sweep, sweep, sweep, and two double-pole single-throw toggle switches I69, I6I, respectively labeled 110 v. line, 220 v. line. Similarly set into and carried by the panel I 44 and adjacent the lower margins thereof are four double-pole single-throw toggle switches I62, I63, I64, I65,

respectively labeled shutter, lamp, blower, and vacuum pump.

Set into and carried by the panel I44 are three bulls-eye type signal lights I68, I61, I68. Similarly set into and carried by the panel I43 are four equally spaced horizontally aligned bullseye type signal lights I69, I10, III, I12.

The sweep counter mechanism I55 comprises a skeleton frame I13 having a horizontal base plate I14 and upwardly extending side plates I15. Flanged over at its opposite ends, and secured to the upper ends of the side plates I15, is a crossplate I16 for supporting, upon its under face, an electromagnet I11 having an enclosing frame I18 and a pole piece I19 projecting outwardly from an end thereof. Swingably mounted upon the frame I18 by means of a pivot stud I80 is a leaf type armature I8I provided at its upper end with an extension arm I82 for engagement in one end of a tension spring I83 secured at its other end upon a tension adjusting stud I84 which projects through an upstanding eye I85 formed upon the upper face of the cross-plate I16. Threaded upon the projecting end of the stud I84 for adjustably shifting it lengthwise with respect to the eye I85 is an adjustment nut I86 and lock nut I81. Rockably and swingably mounted upon the pivot stud I80 m an actuating arm I88 provided intermediate its ends with an elongated aperture I89 for loose fitting engagement with a pin I90 fixed in and projecting outwardly from the armature I8I. Below the aperture I89, the actuating arm I88 is provided with an offset bend I9I and, below the latter, is apertured for engagement with one hooked end of a tension spring I92, which is, in turn, hooked at its other end around an upstanding post I93 mounted in the base plate I14 upwardly from, and to one side of, the armature I8I, so that its axis will extend at a substantial angle to the path of movement of the armature I8I and thereby urge the actuating arm I88 laterally outwardly from the side face of the armature I8I. Below the offset bend I9I, the actuating arm is provided with a downward extension I94 terminating just above the frame plate I14 and adapted, upon forward movement of the armature I8I, for edgewise engagement with one of the teeth of a ratchet wheel I95 formed with an integral hub portion I96 bearing upon its downwardly presented end face against the upper face of the frame plate I14 and being pinned to the upper end of a vertical shaft I91 journaled in and extending downwardly through the frame plate I14, and disposed encirclingly around the lower portion of the hub I96 is a spiral spring I98 secured at its lower end to the frame plate I14 and at its upper end to the ratchet wheel I95. At its lower end, the shaft I91 is, in turn, also journaled in a dielectric terminal plate I99, which is secured in downwardly spaced relationship beneath the frame plate I14 by means of a plurality of threaded studs 200 and spacer sleeves 20I.

Mounted upon one of the side plates I15, and projecting inwardly over the ratchet wheel I95, is a resetting mechanism 202 comprising a magnetic coil 203 and a stationary pole piece 204 secured within a frame 205, which is, in turn, provided with an outwardly projecting, preferably integral, tongue portion 206 having an integral stop arm 201 bent over approximately at right angles to the tongue portion 208 and extending across, and in outwardly spaced relationship to. the pole piece 204. Swingably mounted upon the tongue 206, and extending between the pole piece 204 and the stop arm 201, is an armature plate 208 projecting at one end, as at 209, beyond the tongue 206 for engagement with one end of a tension spring 2I0, which is, in turn, at its other end, connected to an ear 2 II struck up from the magnet-frame 205 for normally urging the armature 208 outwardly away from the pole piece 204 and against the stop arm 201. At its other end, as at 2 I2, the armature bears against an actuating bar 2I3 mounted rigidly in and extending from a pawl 2 I4 pivoted at its mid-portion upon an upstanding stud 2I5 mounted in the frame plate I14. The pawl 2I4 is provided at one end with a tongue 2I6 suitably shaped for engagement in the interdental spaces of the ratchet wheel I95 and at its other end is provided with an outwardly extending arm 2I1 apertured for receiving one hooked end of a tension spring 2I8, which is, in turn, at its other end, suitably fastened to the side plate I15 for normally urging the pawl 2 I4 into retentive engagement with one of the teeth of the ratchet wheel I95.

It will be apparent that, as the actuating electromagnet I11 is energized, the armature I8I and its associated actuating arm I88 will be swung inwardly toward the pole piece I19 from the position shown in full lines to the position shown in dotted lines in Figure 16, advancing the ratchet wheel by a distance of one tooth, so to speak. Because the actuating arm I88 is more or less loosely mounted upon the stud I and is free to rock laterally, it will swing slightly toward the armature I8I along the pin I during this advancing movement so as not to bind the tooth of the ratchet wheel I95. When the current energizing the electromagnet I11 is interrupted, the armature I8I will be released and the actuating arm I88 will be pulled backwardly into original position for engagement with the next successive tooth of the ratchet wheel I95. It will thus be evident that each time the electromagnet I11 is energized, the ratchet wheel I will be advanced a single tooth or step. Furthermore, it will be evident that, as the ratchet wheel I95 is advanced, the spring I98 will be placed under increasing tension and will return the ratchet wheel I95 to its original position upon release or disengagement from the pawl 2I4.

When the coil 203 is energized, the armature plate 208 will be swung inwardly against the pole piece 204 and the extended end 2I2 of the arm 208 will bear against and swing the actuating bar 2I3 of the pawl 2I4 outwardly, disengaging the pawl 2I4 from, and thereby releasing, the ratchet I95, which will thereupon be returned to initial position under influence of the spring Pinned to the lower end of the shaft I91 is a conductive disc 2I9 bearing upon its under face against a spring-pressed conductor button 220, which is mounted in the dielectric terminal plate I99. Secured to, and extending outwardly from, the conductive disc 2I9 is a conductor arm 22I, which is bent downwardly and terminates in a contactor shoe 222 which sweeps over a series of thirty-three contact buttons 223 mounted in a uniformly spaced circular series upon the upper face of the dielectric terminate plate I99 along an arc concentric with the shaft I91. It should be noted in this connection that the several buttons 223 are so spaced from each other that the contactor shoe 222 will move successively from one such button 223 to the next adjacent button 223 as the ratchet wheel I95 progresses step by step.

The cycle selector switch I55 comprisesa circular dielectric base plate 224 rigidly bolted by means of pairs of screws 225 to the rearwardly presented ends of oblong-rectangular mounting posts 226, which are, in turn, rigidly secured by means of mounting screws 22"! to the inner face of the panel Hi4, so that the base plate 224 is held in rearwardly spaced parallel relation thereto. Mounted concentrically in, and extending through, the base plate 224- is a bearing sleeve 228, and similarly mounted in the panel I44 in axial alignment with the bearing sleeve 228 is a second identical bearing sleeve 2 29-.

Also mounted in the dielectric base plate 224, in

a uniformly spaced circular series concentrically around the sleeve 228, are twelve contact buttons 2-30, and shi-ftably mounted in, and extending through, the dielectric base plate 224- is a spring-pressed conductor button 231. Rotatably mounted in, and extending through, the sleeves- 2-2'8, 2-29, is a rotor shaft 232', which is: threaded on its inner end and provided with a pair of lock nuts 2-3 3- and a cupped spring washer 234. At its opposite end; the shaft 23-2 projects outwardly beyond the sleeve 2-29 and is rigidly molded into a Bakelite-knob 235 terminating in an indicator pointer 236, which sweeps over a dial 231 stenciledor otherwise imprinted upon the face of the panel 144 and having indicator numerals ranging from one to twelve, which are more or less aligned, each with one of the contact buttons 2-30, so as to correspond thereto. Along that portion of its length which lies between the panel I44 and the dielectric base plate 224, the shaft 232 is provided with a tight-fitting dielectric sleeve 232' for supporting the tubular hub portion 233 of an electrically conductive rotor drum 235, the hub portion 238 and dielectric sleeve 232 being pinned rigidly tov the shaft 232 by meansof a dielectric pin 24!). The rotor drum 239 integrally includes an electrically conduc tive and tubular flange or skirt 214i, which is.

adapted for engagement, along its. peripheral or rearwardly' presented edge, with the contactor buttons 23!! and is provided. at one segmental portion of its total circumference with a cutaway portion or so-called blank spot 2-42. The width of the. blank spot 242 is slightly greater than the center-to-center distance. between any two adjacent contact buttons 23!) plusv the diametral width of a single contact; button, so that one of the. twelve contact buttons 230 will always be left out of contactive engagement with the peripheral edge of the drum skirt 24 l. The blank spot 242 is furthermore aligned with the pointer 236, so that, when the latter is turned into registration with any selected one of the indicator numbers onthe dial 231, the contact button 239,. which corresponds with that number, will be in alignment with the blank spot 2-42 and, therefore, be out of contactiveengagement. The inner flat face of the drum 239 contactivel-y rides against the contactor shoe 23!, so that a circuit may be completed through the shoe 23! and the drum 2-39 to the remaining eleven contact points 230, all as may best be seen in Figures 2-1 and 22 and for purposes presently more fully appearing.

Suitably suspended from the top frame 2 is a conventional switch box M3 carrying two doublepole double-throw relays 244, 245, which may be, for convenience, referred to, respectively, as forward direction relay and backward direction relay. Similarly suspended from the top frame 2 is a switch box 246 carrying an automatic reversing switch 241 having actuating coils 241 and 24'!" respectively associated with singlethrow double-pole switches at, 2. Also mechanically associated with the switch a for actuation by the coil 24'!" is in auxiliary single-throw single-pole switch b. Similarly suspended from the top frame 2 is a conventional type of main line fuse switch 248. Also suspended from the top frame 2 is a switch box 249 containing a double-pole double-throw relay 250,v which, for convenience, may be designated as the sweep start and stop relay. Likewise suspended from the top frame 2 is a switch box 25] containing a four-pole double-throw relay 252, which, for convenience, may be designated as the vacuum pump relay. Finally, a large switch box 253 is suitably suspended from the top frame 2 and contains a three-pole double-throw lamp control relay 2-54 and a thermostatic relay 255' connected in series with one lead to the blower motor 64 and being in temperature responsive relation to the lamp circuit so as to cut out the blower motor 64 when the temperature of the lamp 62 drops below a predetermined point and cut the blower motor 64 back in again when the temperature of the lamp 6-2 rises above the predetermined point. Mounted upon the sub-frame shelf 5 is a transformer 255 for supplying current to the light source or lamp tube 62. All of the foregoing electrical components are connected as schematically shown in the wiring diagram, Figure 23. Also shown in the wiring diagram, Figure 23, are two conventional main line safety fuses 256, 256', which are located within the main line fuse switch 248.

Bolted upon the forwardly presented vertical face of. the base ll] of the cylinder holding apparatus B is a manually operable vertically shiftable plunger pin 251, which drops down and fits snugly-into a suitable aperture 258 drilled in the bed-plate 1 and actuating-1y engages a microswitch 259 or safety switch, as it may be called, which is bolted upon the under face of the'bedplate 1.. It should be noted in this connection that the aperture 258 is so positioned that the plunger pin 25! will only stop thereinto when the cylinder holding apparatus B is pushed back into so-called exposure position, that is to say, the position in which the axis of the mandrel I5 is precisely aligned with the axis of the trunnions 42. Also mounted in the switch box 253 is a shutter control relay 260 having an actuating coil 260". Finally, the bed-plate is provided upon its forwardly presented margin with two rigidly bolted upwardly projecting stock plates 26!, 261 for abutting engagement with the forwardly presented face of the base Iii when the cylinder holding apparatus B is pulled forwardly to cylinder resetting position to prevent the cylinder holding apparatus B from.- being accidentally pulled too far forwardly and accidentally dropping over the forward edge of the bed-plate I, as best. shown in Figure 1 and 2.

The operation of the various circuits and electrical components is as follows:

Assuming that the negative n has been properly installed in the negative holding clamps I1, H, and the cylinder holding apparatus B has been pushed back to its operative exposure position, the safety switch 259 is closed by the locking plungers 251. This safety switch 259 operates to disconnect the lamp moving circuit to the motor 86 when the plunger 25'! is lifted up out of place so as to prevent lampmovement when the cylinder holding apparatus B is moved forwardly into cylinder resetting position. Consequently, when the cylinder holding apparatus B is returned to "exposure position and the plunger 251 drops in the aperture 258, engaging the actuating member of the safety switch 259, the latter is closed and the circuit to the motor 86 is conditioned for energization. The main line switch 248 may then be closed and the switches I6 I66, are then turned on.

Thereupon, the operator will set the machine A for any desired sweep degree by manually operating the correspondingly selected one of the sweep switches I51, I58, and I59. For instance, if a 60 angle of sweep is desired, sweep switch I51 will be turned on. Incidentally, it may be noted that the sweep switch I53 acts as a limit switch in case the sweep switches I51 and I58 are inadvertently left on, the point being that the 180 sweep switch I53 merely operates as a reversing switch to prevent rotation beyond an angle of 90 on either side of zero position. If, then, a sweep of 60 is desired, in order to cover the narrowest exposure area, switch I51 will be closed and switches I63, I64, are turned on, so that the light 62 will be warmed up. Next in order, the vacuum pump switch IE is turned on. The blower switch I64 can be turned on and off at will to close the circuit to the blower motor 64. The lamp switch I63, which controls the lamp 62, is connected in series with the blower switch I64, so that the lamp 62 cannot be turned on unless the blower motor 64 is on; hence, switch I63 is actually in series with switch I64, so that closure of the switch I64 is a condition precedent to closure of the switch I63.

The vacuum pump switch I65 is then closed, energizing the vacuum pump 23. Whether or not the vacuum pump 23 is energized before or after the lamp 62 is turned on is optional. It should be noted in this connection that the vacuum pump circuit is independent of the exposure circuit because the vacuum pump 23 must be on when the negative n is placed under the negative holding bars I8.

Next, the number of sweeps is established by setting the cycle selector switch I56. It should be noted that each of the contact buttons 230 of the switch i56 is connected in series with a group of three successive contact buttons 223 on the sweep counter I55. Thus, when the pointer 236 is turned to any one of the numbers on the dial 231, the contact button 230 corresponding to that number will be the one which is out of contact, that is to say, opposite the blank spot 242 of the rotor drum 239, and the particular set of three contact buttons 223 which are in series with such disengaged contact button 236 will be dead, so to speak. The rotor drum 239 of the cycle switch I56 is furthermore electrically connected to the line through other control circuits presently to be described.

The machine A is now set to operate and is placed in operation by pressing the button of the switch I5I, thereby momentarily energizing coil 263, returning the sweep counter I55 to zero position, if, by chance, it is not already in such position. The button of switch I52 is next pressed, momentarily energizing coil I11 to move the contactor shoe 222 of the sweep counter I55 to the first contact point thereof. Thereupon, the button of the switch I54 is pressed, thereby energizing the circuit to relay 250.

Since the switch I6I is closed, one side of the relay 250 will be connected through the switch I6 I' to the line and the other side of the relay 250 16 will be connected through the other side of the switch I6I to the line through the switch I54.

The blade of the switch I54 is connected in common with the blade of the switch I53 to one terminal of the switch I5 I. It will be noted that normally, when the switch I5I is open, the blade thereof is in contact with this last-named contact point and will energize this line to the blades of the switches I53 and I54. This is a safety device, so that, when the switch I5I is pressed in order to reset the sweep mechanism, the electrical connection to the blades of the switches I53 and I54 will be broken, thereby shutting down the machine A if, by accident, it has been left in operation.

The blade of the switch I5I is connected to the blade of the switch I I5, which is one of the three series connected sweep limit switches actuated by the screw driven slide block I08. It should be noted that this switch I I5 corresponds to the limit, i. e., it is one of the forward limit switches controlling the sweep movement. The blade of this switch I I5, when the switch I I5 is open, rests upon one contact point which is connected to the blades of the other two forward limit switches I I6, I I1, and to one of the contacts of the switch I59 (180 sweep switch). It should be noted that this particular contact point is also in series through the blades of the switches H6, H1, and with the corresponding poles of the switches I51, I58, so that, whichever one of these is closed, a circuit will be made from the blade of the switch I I6 through to the contact point of the forward direction control relay 244.

It should also be noted that the blade of the switch I5I is connected directly to one blade 01' the switch I6I; hence, the blades of the switches I53, I54, are always connected through the blade of the switch I5 I' to the line.

When the coil 250' of the relay 256 is momentarily energized by closure of the switch I54, the relay 250 is closed and thereupon holds itself in closed circuit position through an interlock control, i. e., the contact which is under the blade normally connected to the line through the switch I54 is permanently connected to one contact of the switch I53 and the blade of the switch I53 normally rests in contact with that contact when the switch I53 is open, so that, after the machine A is in full operation, the switch I53 may be pressed, opening that circuit, breaking the flow of current to the interlock contact point, de-energizing the coil 250', and allowing the relay 250 to open itself.

The switch I53 serves as an emergency stop device, and, when pressed, will arrest movement of the machine without resetting any of the controls or disturbing the condition of the sweep counter switch I55 or the directional relays 244, 245. This makes it possible for the machine A, after an emergency stop, to be started exactly where it left off.

As the relay 250 closes, the machine A will immediately commence operation and the following sequence of electrical contacts will take place. The main blade of the relay 250 is connected to the line in the same manner as the blades of the switches I53, I54, and, when closed, transmits current through its contact point to one side of each of the reversing switch coils 241', 241". For purposes of convenience, these reversing switch coils 241' and 241" will be referred to, respectively, as the forward and backward reversing switch coils. The other terminal of the "backward reversing switch coil 241" is connected directly to the normally open terminal of the backward direction relay 245 and the corre sponding terminal of the forward reversing switch coil 241' is connected to the normally open contact of the forward direction relay 244. The normally closed contact of the forward direction relay 244 is connected in series with one terminal of the actuating coil 245 of the backward direction'relay 245. The other terminal of the coil 245' is connected to the cycle switch I56 and to the first contact point on the sweep counter I55. Since the sweep set switch I52 has been closed and the arm of the sweep counter I55 is in contact with the first contact point, the latter contact arm is connected in series with the blades of the switches I51, I58, and I59.

Since the switch I51 has been closed, a circuit is completed through the contact point of the switch I51 through the forward limit switches II9, I29, and I2I. Thus, the contact arm of the sweep counter switch I 55 will be connected through the left hand contact (reference being had to Figure 23) of the switch I51 to the normally closed contact point of the switch I I9, and through the blade thereof to the normally closed contact of the limit switch I2I and through the blade thereof down to the common hot lead which extends through the blade of the switch I6I to the main line. The coil 244 of the relay 244 is, therefore, energized and the relay 244 closes. The blade of the relay 244 is conected to one pole of the safety switch 259. As above pointed out, when the cylinder holding apparatus B is in exposure position and the plunger 25'! is in the aperture 258, the switch 259 will be closed, so that the contact point, which is connected to the blade of the relay 244, will be connected through the safety switch 259 to the line through the switch I6I. On the other hand, if the cylinder holding apparatus B is not in exposure position and the plunger 25'! is out of place, the safety switch 259 will be open and no current will flow to the blade of the relay 244. On the contrary, the current will flow through the blade of the switch 259 to the other contact point of the switch 259 and thence to the light I68, which will thus be turned on to indicate the fact that the cylinder holding apparatus B is not in exposure" position. Assuming that the table is in exposure position and the switch 259 is closed, current will flow through the closed blade of the relay 244 and the contact thereof direct to the forward coil 24'! of the reversing switch 241, which thus becomes energized, closing the switch 241 in the forward position, transmitting current from the line to the motor 86 in such a direction as to cause the motor to run in the forward direction, and, as previously pointed out, the brake solenoid I29 is energized to shift the brake shoes I24 into released position.

The shutter control relay 269 is connected in series with the switch I62 and the shutter solenoid 82 and its actuating coil 259' is connected in parallel with the motor 86 and solenoid I29. Thus, when the circuit to the motor 86 is energized, the coil 269' of the relay 269 will be energized, so that the relay 269 will be closed, connecting the shutter solenoid 82 to the 119 volt line and the shutter plates 69, 69', will be electrically opened as the sweep starts. When the coil 259' of the relay 269 is again deenergized, as will be presently explained, the relay 269 opens again and the shutter plates 69, 69, are closed. It is important to note that the shutter is opened only when the motor 86 is running and is always shut when the motor 86 is off, except that provision is made through a manually operable switch 262, also mounted in the panel I44, whereby the shutter solenoid 82 can be energized independently of the automatic circuits, so that, if the operator desires, 'he can manually open the shutter plates 69, 69'.

As the main drive motor 86 operates, the lamp assembly L will move forwardly through an arc of 30 and simultaneously the lead screw I95, which is also driven by the motor 86, will traverse the slide block I98 to the left and engage the fixed contact and will strike the roller of the switch I I9, closing it by moving the blades thereof from normally opened position to closed position. This will break the circuit, which, up to now, has been established to the coil 244 of the forward relay 244 and, at the same time, will close a circuit to the coil 245 of the backward relay 245. As the circuit is broken to the coil 244' of the forward relay 244, the blade thereof swings back into normally open position and contacts its open position contact point, thereby closing a circuit through the safety switch 259 to the line, so that the coil of the backward relay 245 will immediately be energized, and, thereupon, the relay 245 closes, transmitting current to the other coil24I" of the reversing switch 241. Upon becoming energized, the coil 241" shifts the reversing switch to its backward position, connecting up the coils of the motor 86 in the opposite direction, so that the motor 86 will drive the lamp assembly L reversely. As the relay 245 closes, it will also close an interlocking contact, so that the relay 245 will remain closed even after the motor 86 has begun to rotate in the reverse direction and the slide block I98 begins to move in the reverse direction away from mechanical contact with the roller III! of the switch H9.

The motor 86, now moving in reverse direction, swings the arms 41, 5|, and associated structure upwardly through an angle of 30 to zero position and then beyond zero position to a position 30 on the other side, whereupon the shoe II4 carried by the slide block I98 contacts the roller I I? of the switch I I1, moving the blade of the switch II'I from its normally closed position to an open position. The interlock of the relay 245 has been connected through one pole of the switch I5! and the blade of the switch III through the switch I I5 to the line; thus, when the switch I I1 is actuated, the circuit to the interlock will be broken and the relay 245 will drop into open position. As the backward direction relay 245 drops into open position, a circuit will again be completed to the coil 244 and the controls will again be reversed so as to cause the motor 86 to move the lamp assembly L in the forward direction. This action is repeated at each limit to and fro, so that the sweep will oscillate through an arc of 60 (30 on either side of the zero position).

This back and forth movement would continue without interruption except for the fact that on each back stroke of the slide block I98 the shoe I I4 will contact the roller I22 of the microswitch I22, momentarily transmitting current from a contact, which is closed when the reversing switch 241 is in backward position, to the ratchet solenoid II'i, giving one impulse thereto and moving the arm of the sweep counter I55 one step forward.

If the cycle switch I56 is set for a single sweep, the contactor shoe 222 will move off of the first contact to the second contact, but this latter contact will not be energized because it will be opposite the blank spot 242 on the drum 239 of the cycle switch I56 and current will not be transmitted to the relay 244 through the arm of the sweep counter I55. It should be noted that the relay 245 is normally held closed by its interlook, so that, when it is operated, it holds itself closed until the limit switch H (or the companion switches I20, I2I, if the machine is set for either 120 or 180 sweeps) is contacted and thrown open. On the other hand, the forward driving circuit through the relay 245 is held closed by the contact arm of the sweep counter I55, which is in parallel with the center microswitch II8 also normally closed. Consequently, when the shoe I I4 carried by slide block I08 upon its backward movement contacts the counter impulse switch and moves the counter arm over to the second or dead contact point, thus breaking the circuit through the switch arm of the sweep counter I55 to the relay 244, a circuit will be momentarily maintained through the normally closed center switch II8, but as the lamp assembly L returns from the backward limit and approaches zero position, the shoe II4 will open the switch I I8 as zero position is reached, stopping the lamp as embly L precisely at such zero position, turning off the motor 85 and immediately applying the brake shoes I24 to the brake drum I23, preventing overtravel past zero position.

As previously described, when the motor 85 stops, the circuit to the coil 260' will be open and the shutter solenoid 82 will be de-energized, returning the shutter to closed position. Thus, when the cycle switch I56 is set on the first or one-cycle contact, that is, for one sweep, the machine A will perform a single sweepand come to a stop. If, however, the switch is set on one of the higher numbers, it will perform any multiple of three sweeps and stop, because each three successive groups of contact points 223 on the sweep counter I55 are connected together.

When the switch II is closed, the light I60 will turn on, indicating that sweep counter I55 has returned to zero position. When the switch I52 is closed, the light I56 will turn off again, indicating the machine A is then ready to start a new cycle of exposure. that the lamp assembly L is in zero position and serves as a safety light, since the machine A is built to fairly close dimensional limits and the cylinder holding apparatus B can only be moved from its exposure position into the forward or cylinder resetting position when the lamp assembly L is in, or rearwardly of, zero position. The fact that the lamp assembly L is properly in zero position is indicated by the fact that the light I61 will b lighted whenever the switch H8 is closed. It will be evident that the light I61 will blink each time the lamp assembly L passes through center or zero position. This blinking function is also important in that it indicates when the lamp assembly L is passing through zero position. Consequently, if some emergency arises wherein it becomes necessary to remove the negative or, for some other reason, pull the carriage forwardly for inspection, the operator can wait until the light I51 blinks before pressing the switch I53, thereby assuring himself that the lamp assembly L is at or rearwardly of its zero position, permitting enough clearance for forward sliding of the cylinder holding apparatus B.

The light I51 indicates The light I68 indicates that the shutter plates 69, 69', are open and is in series with the automatic shutter opening circuit, so that, when the switch I52 is closed, placing the shutter motor 52 on automatic operation, the light IE9 will re lit to indicate this condition. Similarly, the lights I10, HI, and I12 are respectively in parallel with the switches I53, I64, and I65 to indicate when such switches are in closed position. It will, of course, be obvious in this connection that the machine A should preferably be installed in a dark or dimly lighted room, so it is essential that the condition of each operational circuit be indicated by a suitable light, and it will also be apparent that these lights I to I12, inclusive, must be covered with a conventional dark room lens.

The foregoing description of operation has been based upon the assumption that the machine A has been set up for 60 sweeps. If sweeps are desired to provide greater exposure time or to cover a greater area of the negative n, the switch I58 will be closed instead of the switch I51. In such case, the shoe II4 of the slide block I08 will, during its to-and-fro travel, pass over the rollers H1 and H9 of the microswitches II1, II9, respectively, without producing any result, but the micro-switches H6 and I20 now become the limit switches and function in the same manner as above described in connection with the switches H1, H9, to alternately reverse the direction of the motor 85. Finally, if a sweep is desired, the switch I59 is closed, leaving the switches I51, I58, untouched and the micro-switches II5, I2I, become the limit switches and take over the functions of the micro-switches H6, H1, H9, and I20.

If desired, a modified form of positioning mechanism may be provided, as shown in Figures 24 to 27, inclusive, comprising front and rear bearing posts 210, 21I, located equidistantly to the front and rear, respectively, of the lead screw I05 and provided upon their upper faces with microswitches 212, 213, respectively corresponding to the previously described micro-switches I I8, I22, and having roller elements 212', 213, located for actuating contact with the shoes H4, H4, carried by the slide block I 08 and nut I09. The slide block I08 is mounted for shiftable travel along the upper rail portion I01 of an L-shaped member I06, substantially similar to the previously described member I06, except that the rail portion I01 is provided with a relatively large clearance aperture 214 which is transversely in line with the center line of the bearing post 21I for permitting passage of a shaft 215, which is journaled at its opposite ends in the posts 210, 21I. At its forward end, the shaft 215 projects outwardly beyond the bearing post 21I and, on such projecting end, is provided with a crank handle 216. Pinned to the shaft 215, along that portion of its length which extends between the bearing post 210 and the handle 215, is a small gear or pinion 211 adapted for meshing engagement with a relatively large spur gear 218, which is, in turn, pinned upon a short jack shaft 219 journaled in, and extending horizontally through, a face plate 280, which is rigidly supported adjacent its lower margins by means of screws 28I and spacer blocks 282 in outwardly spaced parallel relation to the front face of the bearing post 210. The face plate 280 is provided centrally of its lower horizontal margin with an upwardly curved U-shaped recess 283 of such size as to provide clearance around the hub of the handle 

